1. Field of the Invention
The present invention relates to an electrophotographic copying apparatus and, more particularly, to an electrophotographic copying apparatus which can perform, in a single step of operation, both transfer of a toner image to a sheet-type recording medium and fixing of the toner image to the recording medium.
2. Description of the Prior Art
As disclosed in Japanese patent Laid-Open Publication No. 2-157883, a typical known electrophotographic copying apparatus has transfer means for transferring a toner image formed in a recording section onto a recording medium such as recording paper, and fixing means for fixing the transferred image to the recording medium, the transferring means and the fixing means being disposed independently at difference locations. The transfer means causes the toner image to be attracted by the paper with a small electrostatic force, and the paper thus holding the tone image with a small force is conveyed to the fixing means. Consequently, a slip tends to occur between the toner particles forming the toner image and the paper during conveyance of the paper from the transfer means to the fixing means, resulting in a degradation or distortion of the image.
Another problem encountered with the known apparatus is that, since the transfer means and the fixing means are disposed separately, the toner image tends to be distorted due to inertia of the toner particles when the leading end of the paper is caught in the fixing means, as a result of difference between the paper transporting speed of the fixing means and that of the fixing means.
In the known electrophotographic copying apparatus, the above-mentioned difference in the paper transporting speed is absorbed by a slack or bend of the paper in the region between the transfer means and the fixing means. Consequently, a considerably large distance is essentially required between these two means, which undesirably increases the size of the whole apparatus.
In addition, copying of image to a recording medium comprising a plurality of sheets, e.g., a notebook, has been practically impossible with the known copying apparatus due to difficulty encountered in conveying such a medium from the transfer means to the fixing means.
Furthermore, in the known electrophotographic copying apparatus, the transfer means and the fixing means are independently mounted on the frame of the apparatus, and so is a developing means for forming the toner image. Consequently, these means have to be handled separately during, for example, maintenance work.
The known electrophotographic copying apparatus of the kind described above, having the developing means, transfer means and fixing means constructed as separate units, suffers from the problem that, since these units have their own periods of maintenance or renewal, the period of the maintenance or other work conducted on the whole apparatus is shorter than that for each of these units. In addition, a troublesome adjusting work is often required to keep these units in good relation to each other in order to maintain a high quality of the copy image.
To discuss this problem in greater detail, assuming here that an electrophotographic copying apparatus has three units: a first unit which is to be renewed for every 10,000 copies, a second unit which is to be renewed for every 15,000 copies and a third unit which is to be renewed for every 20,000 copies. Thus, the lives of the first, second and third units expire when they have been operated to make 10,000 copies, 15,000 copies and 20,000 copies, respectively. Consequently, the second unit has to be renewed after the production of only 5,000 copies after a maintenance work which was conducted for renewing the first unit after production of the initial 10,000 copies. If the expected performance of the copying apparatus has not been recovered despite the renewal of the second unit, the user will be at a loss as to what should be the cause and may attempt to renew the first and/or third units even though the lives of the first and third units have not yet been expired. Consequently, the period of the maintenance is shortened to 5,000 in terms of the number of copies produced. Needless to say, such a frequent renewal of units leads to wasteful use of these units.
In addition, delicate adjustment of the units in relation to each other, which has to be done each time a separate unit is renewed, cannot be executed completely satisfactorily unless the adjustment is done in the factory in which the apparatus was produced or by a skilled maintenance engineer.
For these reasons, electrophotographic copying apparatuses in user's offices are not always used in their best conditions.